Conventional golf balls can be divided into two general classes: (a) wound-core golf balls and (b) solid golf balls. Wound-core golf balls with balata (trans-polyisoprene) covers were typically preferred by professional and low handicap amateur golfers prior to recent developments in solid core golf ball technology. Wound balls with balata covers provide a combination of distance, high spin rate, and control that formerly was not available with other types of golf balls, though this is no longer the case. Nevertheless, the soft balata cover is still preferred by many. However, balata is easily damaged in normal play and thus lacks the durability required by the average golfer.
Solid golf balls include balls with a solid core and usually one or more additional layers. One-piece balls are easy to construct and relatively inexpensive but have poor playing characteristics and are thus generally limited for use as driving range balls. Two-piece balls are constructed generally with a solid core, formed of a solid sphere which typically comprises a polybutadiene-based compound, and a cover, usually an ionomer composition. Ionomer resins are generally understood as thermoplastic polymers that are ionically crosslinked, and which may contain both hydrogen and ionic bonds. Ionomers are typically derived from copolymers of an olefin, e.g., ethylene, and an α,β-unsaturated carboxylic acid, e.g., acrylic acid, methacrylic acid, or maleic acid, that are partially neutralized with metal ions such as sodium, lithium, zinc, or magnesium ions, as disclosed in U.S. Pat. Nos. 3,264,272 and 3,404,134. Examples of commercially available ionomer resins include, but are not limited to, SURLYN® from Dupont de Nemours and Company, and ESCOR® and IOTEK® from Exxon Corporation. These ionomer resins are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization. Two piece balls with ionomer covers are generally easy to manufacture, extremely durable, have good shear resistance, and are difficult to cut. However, this durability results from the hardness of the ionomer, which gives such balls a very hard “feel” when struck, which many golfers find inferior to the softer “feel” of a balata covered ball. In addition, the hardness of the ionomer gives the balls a lower spin rate, making these balls more difficult to control. Accordingly, two piece balls are regarded by expert players as having limited playing characteristics.
Multi-layer solid golf balls include a solid core, one or more intermediate layers, and/or a cover of one or more layers. These balls are regarded as having an extended range of playing characteristics. A variety of multi-layer golf balls have been designed by manufacturers to provide a wide range of characteristics, such as durability, compression, velocity, “feel,” and spin. These characteristics can be optimized for various playing abilities by modifying the types and compositions of the layers in the balls. Various polymer formulations and combinations have been prepared, largely focusing on modifying the properties of ionomer compositions by forming ionomer blends.
For example, U.S. Pat. Nos. 4,884,814, 5,120,791, 5,324,783, 5,415,937 and 5,492,972 disclose ball compositions which are blends of high-hardness ionomers and low-hardness ionomers. Other patents disclose blends of ionomers and nonionic polymers, such as U.S. Pat. Nos. 5,397,840, 5,516,847, 5,703,166. These patents attempt to overcome the inherent immiscibility of ionomers and nonionic polymers by adding polar functionalities to the nonionic polymers (see, e.g., U.S. Pat. Nos. 4,986,545 and 5,359,000), or by adding compatibilizers to provide or enhance the compatibility of the two polymer species (see, e.g., U.S. Pat. Nos. 5,155,157 and 5,321,089, and Japanese patent application 6,192,512 (1994)). Still other patents disclose blends of normally immiscible or poorly miscible non-ionomer polymers with compatibilizers (see, e.g., U.S. Pat. No. 5,422,398).
U.S. Pat. No. 4,692,497 discloses a golf ball and material thereof formed by curing a diene polymer including polybutadiene and a metal salt of an alpha, beta ethylenically unsaturated acid using at least two free radical initiators.
U.S. Pat. No. 4,526,375 discloses golf balls having improved low temperature impact resistance including a cover composition having an ionic polymer with at least two different metal ions in one molecule.
U.S. Pat. No. 5,692,974 discloses compositions using cationic polymers having positively charged quaternary ammonium groups. The cationic groups, preferably present in cationic polyurethane polymers, impart improved characteristics to golf ball covers formed therefrom.
U.S. Pat. No. 5,252,652 discloses a one-piece or multi-layered golf ball core with improved flying performance from a rubber composition comprising a base rubber, preferably 1,4-polybutadiene with a cis- content of at least 40 mole percent, an unsaturated carboxylic acid metal salt, an organic peroxide, and an organic sulfur compound and/or a metal salt thereof. The organic sulfur compound and/or a metal salt is typically present in an amount from about 0.05 to 2 parts per hundred by weight and the organic peroxide is typically present in an amount from about 0.5 to 3 parts per hundred by weight of the total polymer component.
U.S. Pat. No. 5,692,974 discloses methods of using cationic ionomers in golf ball cover compositions. Additionally, the patent relates to golf balls having covers and cores incorporating urethane ionomers. Improved resiliency and initial velocity are achieved by the addition of an alkylating agent such as t-butyl-chloride which induces ionic interactions in the polyurethane to produce cationic type ionomers.
British Patent No. 2,321,021 discloses a solid golf ball having a core and a cover formed on the core and having a two-layered cover construction having an inner cover layer and an outer cover layer. The outer cover layer is comprised of a rubber composite that contains 0.05 to 5 parts by weight of an organic sulfide compound. The core rubber composition comprises a base rubber, preferably 1,4-polybutadiene having a cis- content of at least 40 percent by weight, a crosslinking agent, a co-crosslinking agent, an organic sulfide, and a filler. The crosslinking agent is typically an organic peroxide present in an amount from 0.3 to 5.0 parts by weight and the co-crosslinking agent is typically a metal salt of an unsaturated fatty acid present in an amount from 10 to 40 parts by weight. The organic sulfide compound is typically present from 0.05 to 5 parts by weight.
European Patent No. 0 577 058 discloses a golf ball containing a core and a cover that is formed as two separate layers. The inner layer of the cover is molded over the core and is formed from ionomer resin. The outer layer of the cover is molded over the inner layer and is formed from a blend of natural or synthetic balata and a crosslinkable elastomer, such as polybutadiene. In one embodiment of the outer layer of the cover, the elastomer is 1,4-polybutadiene having a cis- structure of at least 40 percent, with the remaining 60 percent being the trans-isomer. A preferred embodiment contains a cis- structure of at least 90 percent and more preferably, a cis- structure of at least 95 percent.
Notwithstanding these efforts, there is no known prior art disclosure of the use in a golf ball of a block copolymer having a saturated rubber block and an ionomer block as provided by the present invention. It has been discovered, surprisingly, that such block copolymers have desirable hydrogen bonding or dipole interactions as well as ionic interactions which can be utilized to impart improved characteristics to golf ball cores, covers, and intermediate layers, such as improved durability and scuff resistance while obtaining a high coefficient of friction and a soft feel, thus curing deficiencies found in the prior art.